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fix: append nonce alongside unsafe-inline instead of replacing it #3842

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fix: append nonce alongside unsafe-inline instead of replacing it #3842

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18 changes: 13 additions & 5 deletions packages/fresh/src/middlewares/csp.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,11 +12,16 @@ export interface CSPOptions {
csp?: string[];

/**
* If true, replaces 'unsafe-inline' with a nonce-based policy for
* script-src and style-src directives. Fresh automatically injects
* If true, appends a nonce to 'unsafe-inline' entries in the policy
* for script-src and style-src directives. Fresh automatically injects
* nonce attributes on inline `<script>` and `<style>` tags during
* server rendering, so this option locks down the policy to only
* allow those Fresh-rendered inline elements.
* server rendering, so this option allows those Fresh-rendered inline
* elements while keeping 'unsafe-inline' as a fallback for older
* browsers that don't support CSP Level 3 nonces.
*
* Note: 'unsafe-inline' is kept in the policy alongside the nonce.
* If you want only the nonce, omit 'unsafe-inline' from your
* directives.
*/
useNonce?: boolean;
}
Expand Down Expand Up @@ -124,7 +129,10 @@ export function csp<State>(options: CSPOptions = {}): Middleware<State> {
const spaceIdx = d.indexOf(" ");
const name = spaceIdx === -1 ? d : d.slice(0, spaceIdx);
if (INLINE_DIRECTIVES.has(name) && d.includes("'unsafe-inline'")) {
return d.replaceAll("'unsafe-inline'", `'nonce-${nonce}'`);
return d.replace(
"'unsafe-inline'",
`'unsafe-inline' 'nonce-${nonce}'`,
);
}
return d;
});
Expand Down
58 changes: 50 additions & 8 deletions packages/fresh/src/middlewares/csp_test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,7 @@ Deno.test("CSP - GET report only", async () => {
);
});

Deno.test("CSP - useNonce replaces unsafe-inline with nonce", async () => {
Deno.test("CSP - useNonce appends nonce alongside unsafe-inline", async () => {
const app = new App()
.use(csp({ useNonce: true }))
.get("/", (ctx) => {
Expand All @@ -109,10 +109,14 @@ Deno.test("CSP - useNonce replaces unsafe-inline with nonce", async () => {
const html = await res.text();
const cspHeader = res.headers.get("Content-Security-Policy")!;

// Should contain nonce directive, not unsafe-inline
expect(cspHeader).not.toContain("'unsafe-inline'");
expect(cspHeader).toMatch(/script-src 'self' 'nonce-[a-f0-9]+'/);
expect(cspHeader).toMatch(/style-src 'self' 'nonce-[a-f0-9]+'/);
// Should contain both unsafe-inline and nonce
expect(cspHeader).toContain("'unsafe-inline'");
expect(cspHeader).toMatch(
/script-src 'self' 'unsafe-inline' 'nonce-[a-f0-9]+'/,
);
expect(cspHeader).toMatch(
/style-src 'self' 'unsafe-inline' 'nonce-[a-f0-9]+'/,
);

// Nonce should not leak as a response header
expect(res.headers.get("X-Fresh-Nonce")).toBeNull();
Expand Down Expand Up @@ -237,7 +241,7 @@ Deno.test("CSP - nonce does not leak as header without CSP middleware", async ()
expect((res as any)[NONCE_SYMBOL]).toBeDefined();
});

Deno.test("CSP - useNonce replaces unsafe-inline in default-src", async () => {
Deno.test("CSP - useNonce appends nonce alongside unsafe-inline in default-src", async () => {
const app = new App()
.use(csp({
useNonce: true,
Expand All @@ -257,6 +261,44 @@ Deno.test("CSP - useNonce replaces unsafe-inline in default-src", async () => {
await res.body?.cancel();
const cspHeader = res.headers.get("Content-Security-Policy")!;

// default-src should have nonce, not unsafe-inline
expect(cspHeader).toMatch(/default-src 'self' 'nonce-[a-f0-9]+'/);
// default-src should contain both unsafe-inline and nonce
expect(cspHeader).toMatch(
/default-src 'self' 'unsafe-inline' 'nonce-[a-f0-9]+'/,
);
});

Deno.test("CSP - nonce only added when unsafe-inline is present in directive", async () => {
const app = new App()
.use(csp({
useNonce: true,
csp: ["script-src 'self'"],
}))
.get("/", (ctx) => {
return ctx.render(
<html>
<head />
<body>hello</body>
</html>,
);
});

const server = new FakeServer(app.handler());
const res = await server.get("/");
await res.body?.cancel();
const cspHeader = res.headers.get("Content-Security-Policy")!;

// script-src (user override, no 'unsafe-inline'): no nonce, no unsafe-inline
const scriptSrc = cspHeader.split("; ").find((d) =>
d.startsWith("script-src")
)!;
expect(scriptSrc).toEqual("script-src 'self'");
expect(scriptSrc).not.toContain("'unsafe-inline'");
expect(scriptSrc).not.toMatch(/'nonce-/);

// style-src (default, has 'unsafe-inline'): nonce appended alongside
const styleSrc = cspHeader.split("; ").find((d) =>
d.startsWith("style-src")
)!;
expect(styleSrc).toContain("'unsafe-inline'");
expect(styleSrc).toMatch(/'nonce-[a-f0-9]+'/);
});
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